Sonja Farak, 35, of Northampton, was indicted Monday by a statewide grand jury on charges of theft of a controlled substance from an authorized dispensary, tampering with evidence and possession of a Class B substance.

"We allege that this chemist violated the trust placed in her by stealing drug evidence from the lab and in some cases replacing the samples with counterfeit substances,” Attorney General Martha Coakley said.

In January, members of the Amherst laboratory contacted State Police to report a discrepancy in the controlled substance inventory held in evidence. The lab stores and analyzes alleged controlled substances seized by local and state police.

Police allege that Farak tampered with drug evidence at the lab. Police said she was in possession of substances that appeared to be cocaine. Farak was arrested at her home on Jan. 19.

Officials allege that Farak also tampered with four drug samples stored at the lab. Authorities allege that in two of the cases, Farak mixed drug evidence samples with counterfeit drugs to hide the theft and that in another two cases, the samples were missing entirely.

According to authorities, controlled substances believed to be cocaine were found in Farak’s workstation and in her vehicle.